Category Archives: Global Temperatures

That is the assertion of a paper in Nature by Carolyn W. Snyder (Snyder, 2016) based on an analysis of the correlation between atmospheric CO2 concentrations and changes in the global average surface temperature (GAST) over the past 800,000 years. Actually the assertion is that the 95% “credible interval” is 7 to 13 degrees Celsius (12.6 to 23 degrees Fahrenheit) Yikes! Even the current scientific consensus value of something on the order of 3 C (5.4 F) (Collins et al., 2013) is frightening when you consider that the difference in the GAST between the last glacial maximum about 20,000 years ago and at present wasn’t much different than that. Continue reading →

Atmospheric CO2 levels are always lower during glacial periods than during interglacials like the one we are in now. During the last glacial maximum 20,000 years ago, for example, they were at 190 parts per million (ppm), whereas during the most recent 10,000 years, almost up to the present, they have been about 280 ppm. [We have now succeeded in raising them to over 400 ppm and still counting, but that’s a different story.] Eric Galbraith and S. Eggleston (Galbraith and Eggleston, 2017) argue that as far as we know, atmospheric CO2 levels have never gone below the typical glacial levels of 190 ppm, even in extended snowball earth conditions. Why not? Well, a carefully-reasoned 2009 paper they cite (Pagani et al., 2009) suggests that even in the mostly warm conditions of the last 24 million years, when CO2 levels fell below 190 ppm, terrestrial plants stopped effectively photosynthesizing, thus they not only stopped removing CO2 from the atmosphere directly, but they also stopped the active root growth which increases the acidity of soils and enhances chemical silicate weathering from the rocks which removes CO2 from the soil, and ultimately from the atmosphere. Galbraith and Eggleston argue that the same thing has been happening during the glacial periods of the last 800,000 years, and extend the argument to the photosynthesis of oceanic phytoplankton. To wit, when CO2 levels get below 190 ppm, CO2 removal from the atmosphere by photosynthesis and chemical weathering is sharply reduced, so they decline no further. Continue reading →

A glance at the graph above, from the University of East Anglia Climatic Research Unit (http://www.cru.uea.ac.uk/), shows that the last two time periods covered (encompassing 2015) are warmer than at any time since 1850. In the prior decade, however, there was much less upward trend, feeding speculation, particularly from climate-change deniers, that all of the warming we have seen since 1900 was largely unrelated to anthropogenic carbon dioxide emissions. There was also speculation from other scientists that the apparent slowdown in warming was statistically “in the noise” and that, in time, there would be a rebound and that the monotonic upward trend since the mid-1970s would soon resume, as it now seems to have. Time will tell, of course, but mainstream climate scientists Fyfe et al. (2016) have just made a new analysis of the early 2000s warming slowdown and pronounce it real and probably largely attributable to the early 2000s’ negative phase of the Interdecadal Pacific Oscillation (IPO) in which intensification of the trade winds lowered sea surface temperatures enough to offset the warming from the ongoing increases in atmospheric greenhouse gases. Continue reading →

At the end of the last ice age as the Earth was warming to its present condition there was an unexplained 1000-year pause and partial reversal in the warming (called the Younger-Dryas stadial). The result was a millennium of very cold weather in the Northern Hemisphere. The cause was widely attributed to the abrupt stoppage of the Gulf Stream; warm water was no longer transported from the equator north past the US east coast and Europe toward Greenland. The physical cause of the stoppage was presumably the melting of the Laurentide Ice Sheet covering Canada; enough freshwater flowed out over the North Atlantic near Greenland, that it formed a thick layer on top of the ocean that was not dense enough to sink through the underlying salt water. It is sinking saltwater off Greenland that drives the major global ocean currents—the Meridional Overturning Circulation (MOC)—of which the Gulf Stream is the last leg. Scientists are somewhat worried that under the current warming conditions, enough meltwater could flow off the Greenland Ice sheet to wreak the same sort of havoc…a much colder North America and Europe in the midst of a generally warming globe. In 2007, Firestone et al. presented an unexpected theory that the trigger for the freshwater outflow 12,900 years ago was an extraterrestrial (ET) impact event—a comet or meteorite—that also directly led to the Continue reading →

Given the constantly fluctuating nature of weather both seasonally and annually, it is often difficult for scientists to show or describe long-term climate changes in a succinct manner. Even if one accepts the hypothesis that humans can have no major effects on global climate change, it is still useful to study climate patterns for predictive purposes. Certain studies have shown how various climate extremes such as rainfall and temperature are expected to increase in future decades, and others have shown overall warming of the planet. In South Africa, there have been strong trends showing heightened extremes of both the lowest and highest temperatures in all stations studied, though the degree of this amplification varied by location (Kruger and Sekele 2013). This has implications for both the wild ecosystems in South Africa and the human populations. Uncharacteristically high or low temperatures can easily catch humans (and other species) off guard, and it is useful to help predict and prepare for these conditions.

There are large deposits of methane hydrates stored in sediments in shallow Arctic waters along continental shelves. Methane is a greenhouse gas that can cause rapid global warming; scientists estimate that its effects are 25 times greater in magnitude than CO2. Additionally, methane can affect Arctic Ocean water pH and oxygen content. When the methane hydrates escape from the benthic sediments, they turn into methane gas. As global temperatures warm, the bottom water in the Arctic could correspondingly rise, which would trigger the release of these methane hydrates. 25 % of hydrates are in shallow and mid-depth waters. Rupke et al. used models to predict both the current temperatures of Arctic bottom water and the future temperatures 100 years from now. Looking at the gas hydrate stability zone (GHSZ), where hydrostatic water pressure is greater than temperature and salinity dependent dissociation pressure, they determined that changes it its thickness will cause the release of both structure one and structure two hydrates. Structure one and two hydrates have different molecular structure and therefore act differently and are unstable under different conditions. 12% of the total estimated 100 Gt C of methane at a sulfate reduction zone thickness of 5m is predicted to be released into the ocean and atmosphere. This will cause little effect on the climate but could raise the pH and hasten oxygen depletion in the Arctic Ocean . —Katherine Recinos

The authors investigated how the temperature of Arctic bottom waters would change in relation to overall warming. They used a hindcast with the ocean/sea-ice NEMO by the DRAKKAR collaboration. This was compounded with a global simulation at ½ degree resolution (ORCA05) and 46 levels. A repeated-year forcing scenario was subtracted from this model. This gave the researchers a map of current water temperatures with deeper oceanic strata and exposed shelves having colder water. A coupled climate model called KCM was then used at a 2 degree ORCA2 31 level resolution. An atmospheric model, ECHAM5 [15] was used to model changes in the atmosphere. These models generated eight 100 year global warming simulations and a 430 year control experiment. They used a 1% increase in CO2 and present day CO2 levels respectively. It took around 50 years for steady trends to develop, but the results showed a pan-Arctic increase of around 2.5 °C per century with the greatest changes along the continental slopes and on the shelves.

As previously mentioned, there are two types of hydrates found in the Arctic; structure I and structure II. Most of the effects considered in this paper are on structure one hydrates, however both types of hydrates are predicted to be affected, especially in shelf regions. Rupke et al. then estimated the amount of hydrates present in Arctic sediments; 900 Gt carbon found north of 60° latitude under a 5m hydrate free zone. The amount of hydrates found globally is estimated at 500-64,000 Gt C. The total methane hydrates that would be released by a greater than or equal to 20 meter decrease in the gas hydrate stability zone would be 100 Gt C, but in the next 100 years only about 12% of that amount will actually be released. Some of the released methane hydrates could become a sediment based carbon sink through microbial anaerobic oxidation (AOM). The remaining methane will travel up through the water column and pass into the atmosphere. On its way some will be transformed into CO2 and will lower ocean water pH by as much as 0.25 units. Combined with acidification from increased CO2 in the atmosphere, oceanic pH could decrease by around 0.6 units.

The Chinese Loess Plateau is a large source of agriculture and home to the Yellow River, and thus plays an important role in Chinese civilization. Understanding how weather patterns and climate change affect the area is key to being able to prevent any major changes in the future. Since the 1960s data have been compiled on the monsoon patterns in the area, however there are few data on temperature changes. This gap is important to close if models and complete records are to be produced. Gao et al. (2012) collected temperature proxies in the Lanjian region of the Loess Plateau, using tetraether lipids from bacteria. Their findings suggest that insolation is the main driver behind temperature changes for the past 110 thousand years (ky). Their data records match up with other local records, as well as with global forcing records. The data the authors compiled will aid in creating more accurate models for understanding possible affects of climate change on the Loess Plateau. –Mathew Harreld

Local and global monsoon patterns are important indicators of climate shifts. On the Chinese Loess Plateau there are some of the best archives of monsoon profiles in the world, allowing scientists to recreate the East Asian Monsoon pattern for the past few million years. This information allows for the recreation and understanding of past local and global climates. Furthermore, the data collected have important implications for predicting future monsoon rainfall variations, especially in global warming scenarios. The Chinese Loess Plateau has a rich archive of surface soil magnetic properties, oxygen–18, and grain sizes, which all contribute to creating rainfall records. Because of the abundance of these proxies the rainfall patterns in the Chinese Loess Plateau are well understood. However, the temperature variations throughout the same periods are not very well documented. Gao et al. attempt to address the issue of missing temperature data by using tetraether lipids from bacteria in conjunction with known climatic forcings. Temperature plays one of the most important roles in understanding a climate, through the use as the primary source to parameterize climate models, through its influence on other proxies, and through its insight on local mountain glacier activities.

Gao et al. compiled data from the Lantian region of the Chinese Loess Plateau. To optimize their data’s accuracy they compared it to recently published, high-resolution data sources. The differences between their data and the other sources are mostly due to general location, and thus different weather affects, and different modelling techniques.

Variation in the Lantian region’s temperature matches closely with Northern Hemisphere absolute insolation maximum at 35°N. Thus, it seems likely that the insolation forcing of the sun and earth’s orbit drives temperature changes in this region. Maximum (94, 72, 22.5 ka) and minimum (105, 81, 58, 10.8 ka) insolations match with Lantian temperature maximum and minimum. The authors propose that insolation has such a large impact because of the postive feed back loop of monsoon intensities being increased greatly by high summer insolations, which then trap more heat, resulting in even higher temperatures. However, increased monsoon strength does not always occur along with higher temperatures because changes in insolation strengths don’t match up with monsoons changes.

Another potential influence on temperature is changes in atmospheric CO2 levels. Increased temperatures coincide with high CO2 levels, and vice versa. This is to be expected on larger time scales, however on the short term it is more difficult to get a accurate understanding. The results found by Gao et al. further suggest the relationship between CO2variation and large scale temperature variations on the Chinese Loess Plateau.

Glacial records from the nearby Tibetan mountain ranges show maximum local glacial advance earlier than global values. This is fairly common throughout the world, and is most likely due to abundant moisture availability and local cold temperatures. And the data compiled by the authors is consistent with other data compiled in the region. Furthermore, the lowest temperatures in the record are around 30 and 22.5 ka, which designates the local last glacial maximum. Temperatures increased rapidly from 22.5 ka years on, increasing about 9°C. This warming in earlier than global values, but this is also not unusual for local climates.

Compiling a record of temperatures in the Lanjian region will greatly enhance understanding of monsoon changes in the past, as well as aiding in creating climate models for the region so we can begin to better understand future changes under climate change. It is clear that insolation is the main drive in temperature change in the Chinese Loess Plateau, and therefore any insolation maximum combined with monsoon changes and other climate change effects might vastly change the Chinese Loess Plateau region.